Disclosures of U.S. Pat. No. 7,789,862 issued to Gale H. Thorne, Jr. et al. Sep. 7, 2010, and other related U.S. Patent Applications describe separating a conventional syringe barrel into two chambers via a plunger valve having a displaceable stem. However, none of the disclosures treat critical system factors associated with placing a dual-chamber syringe system in commerce. Not only is a dual-chamber syringe required to keep fluids in each chamber of the syringe disparate and deliver only liquid chamber contents sequentially, but other concerns and factors must be considered to make a dual-chamber syringe system viable. A number of system responses to those concerns and factors yield novel methods and devices as part of the system disclosure disclosed herein.
As disclosed in referenced U.S. Patent Applications from which this disclosure continues, dual-chamber syringes commonly comprise a plunger valve which is normally closed and selectively opened for transmitting fluids from a disparate chamber within the syringe. However, in medical practice, dual-chamber device efficacy and safety requires more to be considered than simply the valve and valve actuation alone, although the valve and selective chamber disparateness are critical parameters. As a system, the following operational parameters should be duly considered:                1. accuracy of measurement of dispensed dose        2. a tamper-evident indicator to provide assurance that system is ready        3. certainty of valve actuation only at a desired point in a medical procedure        4. assurance that no back-flow or reflux occurs as dispensing is completed        5. indicia provided upon the barrel of the syringe clearly depicts needed information and is neither confusing nor perplexing        6. monitoring of critical safety parameters        7. compatibility with preferred sterilization procedure        8. number of fluid transfer steps required to fill or mix liquids in a distal chamber        9. closed system operation when handling hazardous or air sensitive materials Safety and efficacy of dual-chamber syringe operation is as much dependent upon the above considerations as a properly operating plunger valve. Such parameters may require different parameter considerations for different modes of plunger valve actuation as is disclosed in detail hereafter.Measurement Accuracy        
With a properly operating plunger valve, there are two conditions which affect measurement accuracy. The first is assurance that all fluid is expelled from a first dispensing chamber before an associated plunger valve is opened to dispense fluid from a second chamber. The second is more critical, because, in conventional syringe operation, measurement of successive volume dispensed is communicated from a plunger through a barrel having indicia marked to measure plunger displacement. As a plunger in a dual-chamber syringe is not mechanically affixed to a stabilizing stem and is, therefore, displaced only by force of fluid within a syringe barrel and variously retarded by internal barrel friction, it is critical that the plunger displacement be “true” and that the plunger not cant during displacement because such canting, though insufficient to permit fluid flow between chambers, could result in inaccurate volumetric measurement due to linear angular displacement of the plunger valve to barrel alignment.
Tamper Evidence
Improper handling of a dual-chamber syringe device can actuate a valve prematurely, resulting in untimely mixing of dose chamber fluid with fluid in a proximal chamber. A tamper evident indicator would preclude using a syringe having such a problem.
Valve Actuation
A plunger valve, opened by displacement of an associated stem, can be inadvertently actuated by inadvertent undue displacement of the plunger valve during a filling process. As stated supra, premature valve actuation can result in mixing of fluids which should otherwise remain disparate. It is also desirable for a clinician to know when a drug dose has been delivered and a following delivery of a flushing liquid has begun.
Reflux
Dual-chamber syringes provide a unique opportunity for reflux occurring not at the end of delivery of fluid from a first of distal chamber, but upon final delivery from the upstream or more proximal chamber. Such reflux may be somewhat curtailed by pressurized air remaining in the proximal chamber, but, more likely, slower to recover compression of elastic members associated with the proximal chamber can result in a negative pressure relative to downstream fluids and resultant reflux. Such reflux is highly undesirable in patient catheter lines and in other applications where retrograde flow can cause blockage. In U.S. Pat. No. 7,789,862 reflux is taught to be assuaged by gas pressure resident in a rear chamber upon final dispensing of liquid therefrom. However, careful analysis of dynamics of actions which generate reflux show that pressure reduction in the rear chamber occurs too rapidly when compared to reflux producing mechanical structure within the chamber to effectively arrest all reflux.
Indicia
Measurement indicia must clearly provide for not only distal chamber volumetric determinations, but for accurate proximal chamber determinations, as well. Further, because of the likelihood of the proximal chamber being pre-filled, volumetric and other identifying indicia are also needed. Because there are two plungers in a dual-chamber syringe and two associated chambers for which volumes should be accurately measured, a number of indicia patterns are possible. Some of the possibilities place special requirements on filling and other factors such as a maximum volume of gas which can be stored in a proximal chamber.
Safety Monitoring
It is standard practice to purge all gas from a syringe prior to dispensing liquid therefrom. While such can be accomplished in a single (conventional) syringe, a dual-chamber syringe may have gas disposed in the proximal chamber due to filling procedures or outgassing. Of course, a plunger valve for a dual-chamber syringe should be designed to separate gas from liquid for a liquid only delivery, such as provided by a liquid only zone device. However, for quality assurance purposes, a control check should be provided for both manufacturing and user testing.
Sterilization Procedure Compatibility
Presently preferred sterilization of pre-filled syringes is by gamma radiation. For this reason all materials, particularly those which are used to form the syringe barrel, valve plunger and stem and plunger and plunger rod, should be selected to be unaffected or at least predictably affected and not operationally impaired thereby.
Fluid Transfer Methods and Apparatus
In such applications as PIXUS storage and retrieval, a system comprising a dual-chamber syringe may profitably enclose both a dual-chamber syringe and an associated distal chamber fluid containing vessel in the same package. Conventionally, if both the syringe and vessel comprise male luer fittings, a female/female luer connector is employed. However, introduction of an additional component adds steps and introduces further opportunity for contamination.
Closed System Operation
There are many reasons for keeping a system closed during a medical procedure (e.g. handling hazardous drugs or air sensitive materials). A male luer fitting of a medical syringe is inherently open when disconnected from a female fitting. For this reason, needleless connectors and male adapters are commonly employed in oncology drug delivery. However, as considered for Fluid Transfer, supra, such generally requires additional components, steps and associated cost.
General
While the above disclosed considerations apply generally to dual-chamber syringes, it is considered prudent to provide an opportunity for evaluating these considerations across a spectrum of dual-chamber syringe designs. In addition, a syringe having structure for an integrally affixed tapered valve is also provided.